Packing for a material and heat exchange column

ABSTRACT

The invention relates to a packing (2) for a material and heat exchange column (1), in which a gas phase and a liquid phase are brought into contact with one another, said packing comprising a multiplicity of identical packing elements (4) which are substantially in the form of a circular hollow cylinder whose annularly extending wall (6) is outwardly concave and inwardly convex and forms two outer edges (11) extending therearound, said hollow cylinder having a high ratio of outside diameter (D) to height (H). In order to reduce the pressure drop and to increase capacity and effectiveness, provision is made for the packing (2) to consist of a multiplicity of superimposed layers (3) of packing elements (4) which lie flat, are distributed randomly in each layer (3), and internally have a free passage cross-section, and in which the ratio of outside diameter (D) to height (H) is from about 6:1 to about 10:1.

This application is a continuation of application Ser. No. 07/469,588,filed May 18, 1990, now abandon.

The invention relates to a packing for a material and heat exchangecolumn in which a gas phase and a liquid phase are brought into contactwith one another, said packing comprising a multiplicity of identicalpacking elements which are substantially in the form of a circularannular hollow cylinder whose annularly extending wall is outwardlyconcave and inwardly convex and forms two outer edges extendingtherearound, said hollow cylinder having a high ratio of outsidediameter to height.

In material and heat exchange columns in which a gas phase is broughtinto contact with a liquid phase a transfer of material and heat occurs,for example absorption with the transfer of a component from the gasphase to the liquid phase, desorption with the transfer of a componentin the opposite direction, or rectification in which components aretransferred in both directions. Since temperature differences usuallyexist, heat transfer also takes place at the same time, for which reasonmaterial exchange columns are always also simultaneously heat exchangecolumns. The gas phase is usually allowed to flow through the columncountercurrently to the liquid phase, and the parallel flow principle isapplied only rarely (while crosscurrent flow is employed only in coolingtowers used for heat exchange). The columns are provided with built-inelements whose purpose is to ensure a high rate of exchange between thegas phase and the liquid phase (efficiency), a high throughput(capacity) for the two phases and the lowest possible pressure drop.

Built-in elements for material and heat exchange columns may be in theform of disordered or ordered packings. Ordered packings preferablyconsist of coarsely folded plates which are arranged with their combscrossing at an angle to one another and to the axis of the column, andwhich are provided with a fine structure in the form of grooves andholes or the like. Their manufacture and their arrangement in the columnare relatively expensive.

Disordered packings consist of individual packing elements which aresimply poured into the column. In comparison with ordered packings,therefore, the arrangement in the column is substantially simplified.Packing elements of this kind include raschig rings, which have beenknown for a long time and which have a ratio of diameter to height ofabout 1:1. A further development thereof consists of so-called pawlrings having small tongues which extend inwards and leave correspondingholes and which have improved capacity considerably. By reducing theratio between diameter and height to 3:1, with the omission of one rowof tongues, pawl rings were able to reduce dead regions.

Development was similar in the case of roof-shaped, semicylindrical,saddle-shaped or similarly shaped packing elements which are likewisepoured into the column in a disordered manner, and which were providedwith increasingly complicated surface shapes in the form of holes, ribs,grooves, projections, depressions, tongues and the like.

Because of their structure, disordered packings show a relatively highpressure drop in the axial direction of the column, which impairs thecapacity of the packing and the effectiveness of the exchange ofmaterial.

This also applies to packings made from packing elements of the kinddescribed in U.S. Pat. No. 3,957,931. These packing elements may be inthe form of circular cylinders, optionally having a concave outersurface, and be provided with inwardly directed ribs, which may alsoproject in the axial direction relative to the cylindrical part. Theribs are intended to prevent the wedging of the packing elements in oneanother when they are poured in, whereby the pressure drop is reducedbecause of the resulting partial alignment of the packing elementsrelative to one another. At least in the case of packing elements madefrom metal by cold-working, the provision of ribs is expensive, and whenthe packing elements are poured into a column the resulting packing isnot a well ordered structure but is random and disordered, containingpacking elements lying both flat and at an angle and standing vertical,thus still giving rise to a relatively high pressure drop.

The object of the invention is to provide a packing of the typedescribed in the preamble, which leads to a reduced pressure drop and toincreased capacity and effectiveness of the exchange of material.

This object is solved in that the packing consists of a multiplicity ofsuperimposed layers of packing elements which lie flat, are distributedrandomly in each layer and internally have a free passage cross-section,and in which the ratio of outside diameter to height is from about 6:1to about 10:1.

The packing elements used consist of a ring similar to a bicycle wheelrim, with a relatively high diameter to height ratio, so that packingelements falling freely onto a flat support assume a position in whichthey lie flat and rest on an edge extending around them. The probabilityof their assuming a vertical position when thus dropped is extremelyslight, since this position constitutes the state of unstableequilibrium which would be overcome by even the slightest vibration orthe like, for example the impingement of other falling packing elements.Through the gradual introduction and distribution of packing elementsinto a column it is thus possible to construct a packing which is formedof superimposed layers of packing elements lying flat and which is thusso to speak ordered in the axial direction of the column, while thepacking elements in a layer are distributed randomly and disorderedlyand are practically always staggered relative to those lying immediatelyabove and below them. With a packing of this kind the pressure drop issubstantially reduced in comparison with a completely disorderedpacking, so that the capacity and effectiveness of the material exchangecan be greatly improved With the same capacity and effectiveness, thepacking volume and thus also the weight of the packing are therebyreduced.

In addition, the packing is produced with the aid of packing elementswhich are easy to manufacture and with relatively low labour costsduring the column filling stage.

Further developments and advantages of the invention can be seen in thefollowing description and in the subclaims.

The invention is explained more fully below with reference to theexamples of embodiment illustrated by way of example in the accompanyingdrawings.

FIG. 1 shows part of a packing in a material and heat exchange column,in which rings staggered in the plane of the drawing are shown whileintersected rings are omitted for the sake of clarity.

FIG. 2 is a partial plan view of the packing shown in FIG. 1.

FIG. 3 shows one form of construction of a packing element for thepacking shown in FIG. 1.

According to FIG. 1, a column 1 contains a packing 2 carried by asuitable base (not shown) and consisting of superimposed layers 3 ofpacking elements 4. A liquid distributor 5 is disposed above the packing2.

The packing elements 4 are in the form of a circular annular hollowcylinder, the wall 6 of which has a substantially uniform thickness andis provided with a concave outer side 7 and a convex inner side 8 whichextend around it. In addition, the ratio of the outside diameter D tothe height H of the hollow cylinder is so great that the packing element4, when poured into a column 1, assumes a position in which it lies flaton the base of the column or on a layer of identical packing elements 4,as illustrated in FIG. 1. The ratio of the outside diameter D to theheight H of the hollow cylinder is preferably approximately between 6:1and 10:1.

If packing elements 4 of this kind are carefully filled into a column 1and spread out, a packing 2 of superimposed layers 3 of packing elements4 lying flat is obtained. Although a packing 2 of this kind has anirregular arrangement of the packing elements 4 in each layer 3, withlonger or shorter distances between individual packing elements 4, whilehowever individual packing elements 4 will also be in point contact witheach other, nevertheless the packing 2 is ordered in the direction ofthe axis of the column.

The effect is thereby achieved that the aerodynamic resistance isreduced, and thus the pressure drop inside the column 1 is lowered, incomparison with a completely disordered packing. As a result of thepartially ordered packing achievable with the packing elements 4,moreover, with the same specific surface the packing elements 4 take upa smaller space, that is to say the packing factor is reduced or thecapacity of the packing 2 can be substantially increased with thepacking volume unchanged.

The inwardly curved wall 6 of the packing element 4 provides the latterwith adequate strength and in addition serves to ensure that it ispractically impossible for a packing element 4 to be jammed in aninclined or vertical position in a horizontal packing element 4 andthus, at least in places, prevent the formation of layers 3, but in sucha position instead would be in unstable equilibrium and would thereforebe tipped over into the horizontal position, corresponding to stableequilibrium, when other packing elements 4 are spread out or fall down.

It is expedient for the section of the wall 6 to have the shape of asector of a circular ring, particularly of a semicircular ring, althoughfor example concavities having the shape of part of an oval are alsopossible.

The inwardly curved wall 6 also brings about a corresponding increase ofsurface area, which has the effect of reducing pressure drop andincreasing effectiveness and capacity.

In addition, the inwardly curved wall 6 has the consequence that theliquid phase flows off without forming accumulations of liquid, so thatthe residence time of the liquid phase in the packing 2 iscorrespondingly short. In the case of substances having a tendencytowards polymerization, it is thus possible to avoid polymerization inthe column 1. Moreover, solids in suspension or otherwise introduced arenot retained by the liquid phase.

In a packing 2 according to FIG. 1 the gas phase always flows frombottom to top in the axial direction of the column 1, and thussubstantially in the axial direction of the individual packing elements4, while the latter give rise to a pressure difference between theregion close to the outer side 7 and the region close to the inner side8, the static pressure p₁ on the outer side 7 being higher than thestatic pressure p₂ on the inner side 8 (similarly to an aircraft wing).As a result, a negative pressure is formed in the interior of eachindividual packing element 4, which on the inside has a free passagecross-section, that is to say is without inwardly directed ribs orsimilar fittings. This leads to intensified gas turbulence and thus tocorresponding crossmixing of the gas phase, particularly as eachindividual packing element 4 is slightly staggered relative to theneighbouring element in the layer above and below it.

Since the liquid phase passes, at least in part, along the bottom edgeof the packing elements 4 until it impinges on the top edge of a packingelement 4 situated therebelow, this brings about a mixing, in thedirection transverse to the axis of the column, of the downwardlyflowing liquid phase. A substantially uniform composition of the liquidphase is thereby achieved over the cross-section of the column.

The cross mixing of the gas and liquid phases has the effect that thedriving gradient of temperature and/or concentration can be utilized inoptimum manner.

Accurate horizontal adjustment of the packing 2, or of the packingelements 4, is not necessary; a slight slope leads to a correspondingoutflow of the liquid phase.

The thickness of the wall 6 may for example be approximately between 0.2and 5.0 mm, while the outside diameters D are generally selected withinthe range between 10 and 300 mm. Without loss of effectiveness, theminimum ratio of column diameter to packing element diameter can thenamount to about 4.6:1, as compared with a minimum of 8 to 12:1 for thecustomary disordered packings, so that packing elements 4 having arelatively large diameter D can be used without disadvantage,particularly for laboratory apparatus.

With packing elements 4 having a smaller diameter D it is found thatsome of these are supported in a vertical or inclined position againstthe walls of the column. In the case of columns 1 of smaller diameters,in which a great deal of liquid normally flows down along the wall ofthe column, this can be advantageously exploited, since they guide theliquid from the wall into the interior of the column. For this purposeit is also possible for packing elements 4 to be accordingly arranged tostand along the column wall, as illustrated in FIG. 1.

The packing elements 4 may be made of various materials, for examplemetal, such as carbon steel, stainless steel, titanium, copper, brass,aluminium or the like, which is expediently cold-worked, or ofthermoplastic material such as polypropylene, polyvinyl chloride,polyethylene or the like, or of ceramics, rubber or glass. The startingmaterial used for their production may be provided, before, during orafter their shaping, with a coarse structure, for example so as to formgas passage openings 9 (FIG. 3) or the like which are not normallyflooded by the liquid phase, and/or with a fine structure in the form ofgrooves, protuberances, depressions, small holes or the like, theformation of these structures depending on the type of shaping processused for the packing elements 4. The packing element 4 may also be madefrom a woven material, for example a woven wire material.

Particularly in the case of packing elements 4 of metal, portions of achannel-shaped section or of a flat strip may each be bent into acircular ring, the concavity optionally being formed at the same time,while a narrow gap 10 (FIG. 3) can be formed between the opposite ends,the width of this gap being substantially smaller than the height H ofthe packing element 4 so that another packing element 4 cannot be jammedor caught in it during the filling of the column 1.

The ends of the portion of section bent into a circular ring may howeveralso be joined together, for example by riveting, soldering, adhesivebonding and the like.

Because of the outwardly concave wall 6 the packing element 4 has twoedges 11 extending around it, one of which may be slightly set backrelative to the other; that is to say the diameters of the two edges 11will be slightly different, so that the falling over of the packingelements 4 into a flat position will be additionally assisted. Thedifference in diameter may be so great that the projection of the centreof gravity of the packing element 4, in its substantially verticalposition, onto a support would lie outside its standing surface.

The liquid distributor 5 in the embodiment illustrated comprises asupply channel 12 for the liquid phase, which overflows therefrom intodistributor channels 13. The distributor channels 13 are provided ontheir bottom side with a row of outlet pipes 14 which have outletopenings 15. The outlet pipes 14 are arranged in groups in such a mannerthat their outlet openings 15 are arranged on a circle corresponding toa packing element 4 disposed therebeneath in the uppermost layer 3 ofthe packing 2. The liquid passing out of the outlet openings 15 isthereby directed onto the packing elements 4 in the top layer 3 andcannot fall freely over an indeterminate distance as a jet through thepacking 2. In order to secure the alignment of the packing elements 4 inthe top layer 3 in relation to the groups of outlet pipes 14 whoseoutlet openings 15 are arranged in a circle, the packing elements 4 inthe top layer 3 may be connected by struts 16 or the like, so that thetop layer 3 of the packing 2 can be inserted into the column 1 togetherwith the liquid distributor 5.

The top layer 3 of the packing 2 may instead also consist of packingelements 4 joined together, a packing element 4 of the first layer 3expediently being disposed under each outlet opening 15.

The top layer 3 forming a unit may at the same time form a holding downmeans for the packing 2, in order to prevent the latter from beinglifted under an excessive gas load. The liquid distributor 5, by itselfor in conjunction with the top layer 3, may also form the holding downmeans, or they may both be components of the holding down means.

In the case of packing elements 4 having a correspondingly smalldiameter the outlet openings 15 or the outlet pipes 14 usually cannot beformed into groups, but it is expedient at least to allocate to eachpacking element 4 an outlet opening 15 which delivers onto said packingelement 4 in the top layer 3 the liquid phase discharged by it.

I claim:
 1. A packing element of circular hollow cylindrical shapedefining an uninterrupted passage for passage of a gas phasetherethrough, said element having an annular wall defining an outwardlyconcave semi-circular shape, an inwardly convex shape and having a ratioof outside diameter to height of from 6 to 1 to 10 to
 1. 2. A packingelement as set forth in claim 1 wherein said wall is of uniformthickness.
 3. A packing element as set forth in claim 1 wherein saidwall has an upper peripheral edge and a lower peripheral edge, saidedges being disposed on different diameters from each other.
 4. Apacking element as set forth in claim 1 wherein said wall has aplurality of openings therein for passage of gas.
 5. A packing elementas set forth in claim 1 wherein said annular wall has a narrow gaptherein to define two spaced apart ends.
 6. A packing comprisingaplurality of vertically disposed layers, each layer having a pluralityof horizontally disposed packing elements disposed therein inside-by-side relation, each said packing element being of circularhollow cylindrical shape defining an uninterrupted vertical passage forpassage of a gas phase therethrough and having an annular wall definingan outwardly concave semi-circular shape and an inwardly convex shape,each said packing element having a ratio of outside diameter to heightof from 6 to 1 to 10 to
 1. 7. A packing as set forth in claim 6 whereinsaid packing elements of each layer are vertically offset from saidpacking elements of an adjacent layer.
 8. In combination,a verticallydisposed column; a packing in said column, said packing having aplurality of vertically disposed layers, each layer having a pluralityof horizontally disposed packing elements disposed therein inside-by-side relation, each said packing element being of circularhollow cylindrical shape defining an uninterrupted vertical passage forpassage of a gas phase therethrough and having an annular wall definingan outwardly concave shape and an inwardly convex shape, each saidpacking element having a ratio of outside diameter to height of from 6to 10 to 1; a distributor above said packing for distributing a liquidphase thereon; and at least one vertically disposed packing elementbetween a wall of said column and said packing to divert a descendingliquid phase on said wall, said vertically disposed packing elementhaving a circular hollow cylindrical shape with an annular wall havingan outwardly concave shape and an inwardly convex shape.
 9. Thecombination as set forth in claim 8 wherein each said packing element ismade of metal.
 10. The combination as set forth in claim 8 wherein saidpacking elements in each layer are connected to each other.
 11. Thecombination as set forth in claim 8 wherein said distributor has asupply channel for a liquid phase, a plurality of distributor channelsextending from said supply channel, and a plurality of outlet pipesextending from each distributor channel horizontally over a respectivepacking element in a topmost layer of said packing, each said pipehaving outlet openings disposed above said wall of said respectivepacking element to direct liquid onto said wall.
 12. The combination asset forth in claim 11 which further comprises a plurality of strutsconnecting said distributor to said topmost layer of said packing.